Cystic fibrosis (CF) is a common autosomal recessive disease caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) (1). CF affects multiple organs, including lungs, pancreas, intestine, liver, sweat glands, gall bladder and male genital tract. Airway infection and inflammation cun'ently cause most of the morbidity and mortality. Although several therapies have improved the lives of patients, current treatments are inadequate and CF remains a lethal disease. Our knowledge about the pathogenesis of the disease, its progression, and the state of the neonatal lung is inadequate. Moreover, despite the potential of gene transfer to be an effective treatment, some of the most fundamental questions remain unanswered. These gaps in our knowledge have hindered attempts to develop better treatments and preventions for CF lung disease. A major impediment to addressing these issues has been limitations of current animal models. Although mouse strains carrying null and missense CFTR mutations have made enormous contributions, CF mice do not develop the airway or pancreatic disease typically found in humans.